1. Field of the Invention
The present invention relates to a clamping unit for machine tools with a housing that can be connected to a machine spindle in a rotationally fixed arrangement, and a screw drive arranged in the housing, wherein the screw drive interacts with a draw rod linked to a power chuck, by means of which rotational movements transmitted to the clamping unit can be converted into translational adjustment movements of the draw rod.
2. Description of the Prior Art
An electrical chuck with a clamping unit of this kind is disclosed in DE 10 2007 044 309 A1. In this case, the circumferential housing only serves to support the ring gear of a harmonic drive; in this configuration, there is no transmission of the rotational movement of the machine spindle onto an actuator. Instead, the actuator takes the form of an electric motor acting on a shaft generator of the harmonic drive, by means of which the rolling screw drive of the draw rod can be driven by means of a steel bush that is provided with external gearing and a dog clutch. The rotational adjustment movements of the electric motor connected to the drive gear of the spline shaft gear unit by means of a belt drive, can be converted into translational adjustment movements of the draw rod, although the electric motor needs to be controlled according to the rotation speed and direction of rotation of the power chuck in order to trigger adjustment movements of the clamping jaws, or in order to retain or change the clamping force. In order to achieve this, so that the clamping unit can be used together with the servomotor as an electric chuck, it is necessary to have an extraordinarily complicated control device, as well as numerous programs in which a large number of parameters must be incorporated.
Quite apart from the very great control complexity, this not only leads to a high susceptibility to malfunctions, but also the investment costs, in particular for the control device and the various programs, are considerable. However, the principal disadvantage is that the control unit has to be adjusted to take account of numerous different existing conditions, thereby placing very exacting requirements on the operating personnel. As a result, the electric chuck of the prior art only has limited practical applications.